2.4 or 5 GHz WiFi

Please keep in mind:

All WiFi routers have a 2.4 GHz band.

Newer routers are often dual-band routers, with 2.4 GHz and 5 GHz bands. And mostly WiFi routers will have factory settings that make 5Ghz WiFi work as a default network connection.

But both of your 2.4 GHz and 5 GHz WiFi bands have the same name (SSID) and password, you will not have any problem connecting to that SSID and adding a new smart home device. 

If two WiFi networks belong to you, usually the 5 GHz WiFi band has '5 or' 5G' in its name, do not connect to that one. You can also log into your WiFi router's admin page on a web browser to check the WiFi settings, such as the WiFi band name and password. You can find the login info at the back of your WiFi router or Google "router's model name admin" to find detailed instructions on Google. 

You can also check from your PC as follows: